The wording of this problem indicates that there was an illustration. Could you possibly share that illustration?
Working without an illustration:
If tan theta = 3, then tan theta = opp/adj = 3/1. This tells us that the opp side is 3 times as long as is the adj. side. Let x be the shorter side, i. e., let x represent the adjacent side; then y is the longer side and represents the opposite side.
Then y = 3x (the opp side is 3x the adj side in length).
To find the actual discount, multiply the discount rate by the original amount 'x'. To find the sale price, subtract the actual discount from the original amount 'x' and equate this to given sale price.